1. Field of the Invention
The present invention relates to a distribution system realized by a service for distributing copyrighted digital material such as Electronic Music Distribution (EMD), a semiconductor memory card, a receiving apparatus, a computer-readable recording medium and a receiving method.
2. Description of the Background Art
A distribution system includes a distribution server, a device for purchasing contents, and a playback apparatus for playing back contents, and gives people living around the world the opportunity to purchase copyrighted material via various global networks. If a personal computer owned by a user is used as the purchasing device, contents are purchased in the following way. The user operates the personal computer, and transmits a purchase request to the distribution server. Upon receiving the purchase request, the distribution server bills the user, and then transmits the copyrighted digital material. The personal computer operated by the user receives the transmitted copyrighted material, and writes it onto the hard disk (HD). If writing is performed correctly, the purchase of the copyrighted material is completed.
The purchasing device performs processing called check-out and check-in. Check-out refers to the process of recording copyrighted material (a first-generation copy) onto a portable recording medium such as a semiconductor memory card or a mini disc. The number of times check-out is performed by the purchasing device can also be limited to a predetermined number, such as three or four. If copyrighted material is recorded onto a portable recording medium using check-out, this copyrighted material can be played back using the playback apparatus. However, once check-out has been performed the predetermined number of times, the copyrighted material can be set in a state in which check-out is not permitted. Check-in, on the other hand, is the process of returning copyrighted material recorded on a portable recording medium to the personal computer. If check-in is performed on a copyrighted material that has been set so that check-out is not permitted, check-out of the copyrighted material becomes possible once more. Check-out and check-in are prerequisites for copyright protection, which prevents reduction in the copyright owner's profits.
The following is a brief explanation of how copyright is protected when check-out and check-in are being performed. A unique identifier, called a Media-ID, is recorded in an area of the recording medium onto which a copy of the copyrighted material is to be recorded, the area being one that cannot be read by a normal user operation. When check-out is performed, contents are encrypted using the media ID unique to the recording medium. Thus, even if an ill-intentioned user copies contents that have been checked out onto one recording medium onto another recording medium, the media ID of the recording medium onto which the contents are copied differs from the media ID that was used to encrypt the contents (the media ID of the original disc). As a result, decryption cannot be properly performed, and copyright is protected.